Many clockwork devices comprising a tuning fork as an oscillator have already been disclosed in the prior art.
As an example, Max Hetzel is at the origin of a large number of patented inventions relating to the use of a tuning fork as an oscillator, which have led to the production of the Accutron (registered trade mark) wristwatch marketed by Bulova Swiss SA.
The Accutron watch however comprises an electronic resonator since each branch of the corresponding tuning fork supports a permanent magnet associated with an electromagnet fixedly mounted on the frame of the watch. The operation of each electromagnet is slaved to the vibrations of the tuning fork by means of the magnets that it supports, such that the vibrations of the tuning fork are sustained by the transmission of periodic magnetic pulses of the electromagnets to the permanent magnets. One of the branches of the tuning fork actuates a ratchet making it possible to rotate the mobiles of the watchwork gear train of the watch.
U.S. Pat. No. 2,971,323, for example, originating from a filing dating from 1957, describes such a mechanism which cannot however be suitable for the production of a purely mechanical watch, that is to say having no electronic circuits. Specifically, a real need exists, in market terms, for purely mechanical timepieces having a working accuracy that is enhanced relative to the known pieces.
It should be noted that the Accutron piece is still currently marketed by Bulova Swiss SA.
Patent CH 594201, originating from a filing dating from 1972, describes a double-oscillator resonator system. Use is made of the frequency stability of the oscillations of a tuning fork by magnetic interaction in order to stabilize the oscillations of a balance wheel of conventional shape, hence having a lesser quality factor than that of the tuning fork. For this purpose, the branches of the tuning fork, on the one hand, and the balance wheel, on the other hand, support permanent magnets arranged so as to interact with one another. The corresponding interaction makes it possible both to sustain the oscillations of the tuning fork and to stabilize the frequency of oscillations of the balance wheel.
However, although this does not appear explicitly in this patent, it is evident that this mechanism is necessarily coupled to a mechanical escapement in order to convert the periodic oscillations of the balance wheel into a one-way movement making it possible to drive the mobiles of a watchwork gear train. Thus, it is likely that the balance wheel is coupled to a conventional mechanical escapement arranged to sustain the oscillations. Consequently, the mechanism described in this document makes it possible to enhance the frequency stability of the oscillations of a balance wheel, but this is done at the price of a markedly increased complexity and space requirement relative to a conventional mechanism with a single oscillator. Moreover, the high quality factor of the tuning fork is only partially used in the proposed solution since, in the end, it is the balance wheel which controls the movements of the watchwork gear train in a manner similar to what is used in the conventional systems.
Alternative solutions, more suited to the spatial constraints specific to the construction of a wristwatch, have also been divulged. Specifically, patent U.S. Pat. No. 3,208,287, originating from a filing dating from 1962, describes a resonator comprising a tuning fork coupled to an escape wheel via magnetic interactions. More precisely, the tuning fork supports permanent magnets interacting with the escape wheel, the latter being made of a magnetically conductive material. The escape wheel is linked kinematically to a power source which may be mechanical or take the form of a motor, while it comprises apertures, in its thickness, such that it forms a variable reluctance magnetic circuit when it is rotated, in relation with the magnets supported by the tuning fork.
Consequently, a permanent interaction of substantial intensity takes place between the tuning fork and the escape wheel, which may be qualified as magnetic locking, such a construction therefore consisting of an escapement that is not free. The provision of power from the escape wheel to the tuning fork in order to sustain the oscillations thereof, even though it is weak, is carried out continuously and constitutes a significant source of disruption from the point of view of the isochronism of these oscillations. Similarly, the guidance of the escape wheel by the tuning fork is carried out continuously.
Thus, the type of interaction used in this construction is similar to a contact which is unfavorable from the point of view of working accuracy.
It will be noted that there is a large number of patents to cover technical solutions based on the reluctance principle. It is notably possible to cite the patents GB 660,581, the filing of which dates back to 1948, the patent GB 838,430, of which the filing dates back to 1955, or even the patent U.S. Pat. No. 2,571,085 of which the filing dates back to 1949.